added new, very powerful and flexible item selector system for whitelists/blacklists
added fail-safe check so items don't get duped when the vanilla "keepInventory" gamerule is enabled for a world
added functionality to hook other plugins, currently supported: MobArena and BattleArena; items won't be kept when a player dies during an arena battle
added "keep-hunger" option to restore the previous hunger level (negative effect for the player)
fixed a wrong entry in the default messages.yml leading to an exception
